Drill and insert for drill having improved centering capability and cutting performance

Abstract

Disclosed are a drill and an insert for a drill having improved centering capability and cutting performance. In the drill of the present disclosure, central relief surfaces of cutting parts are processed as flat relief surfaces, and outer circumferential relief surfaces continuing from the center part to the outer circumferential surface of the drill are processed as curved relief surfaces, thereby enhancing the centering capability of the drill and minimizing the generation of drill vibration and burrs. In addition, in the drill of the present disclosure, the outer relief surfaces of the drill in contact with a hole to be drilled are processed such that an angle between the tangential lines of the outer relief surfaces is constant regardless of the size of the outer diameter of the drill, thereby achieving consistent performance of the drill despite change in the outer diameter of the drill.

1 . A drill having a plurality of cutting parts and flutes formed alternately, the drill comprising:
 cutting parts comprising central relief surfaces being in contact with a chisel edge and processed as flat surfaces, and outer circumferential relief surfaces formed by extending from the central relief surfaces in directions toward an outer circumferential surface of the drill and configured as curved surfaces, each of the curved surfaces having at least one radius.   
     
     
         2 . The drill of  claim 1 , wherein a point angle between the outer circumferential relief surfaces in contact with the central relief surfaces is the same as a central point angle between the central relief surfaces, wherein the central point angle is an angle defined by the central relief surfaces. 
     
     
         3 . The drill of  claim 2 , wherein each of the central relief surfaces and each of the outer circumferential relief surfaces are divided into a first relief surface in contact with a cutting edge and a second relief surface extending from the first relief surface and having a relief angle larger than a relief angle of the first relief surface. 
     
     
         4 . The drill of  claim 1 , wherein a central point angle between the central relief surfaces of the plurality of cutting parts is set to be 140° or less, and an outer circumferential point angle between the outer circumferential relief surfaces of the plurality of cutting parts is set to be 140° or more, wherein the outer circumferential point angle is defined by tangential lines of the outer circumferential relief surfaces meeting the outer circumferential surface. 
     
     
         5 . The drill of  claim 4 , wherein despite change in a size of an outer diameter of the drill, the outer circumferential point angle is set to be constant by changing at least one selected from a radius of the curved surface of each of the outer circumferential relief surfaces and a length of each of the central relief surfaces in a direction toward the outer circumferential surface. 
     
     
         6 . An insert mounted to an insert insertion part of a drill, the insert comprising:
 a plurality of cutting parts in contact with a chisel edge, wherein the cutting parts comprise central relief surfaces in contact with the chisel edge and processed as flat surfaces; and outer circumferential relief surfaces formed by extending from the central relief surfaces in directions toward an outer circumferential surface of the insert and configured as curved surfaces, each of the curved surfaces having at least one radius.   
     
     
         7 . The insert of  claim 6 , wherein a point angle between the outer circumferential relief surfaces in contact with the central relief surfaces is the same as a central point angle between the central relief surfaces, wherein the central point angle is an angle defined by the central relief surfaces. 
     
     
         8 . The insert of  claim 6 , wherein each of the central relief surfaces and each of the outer circumferential relief surfaces are divided into a first relief surface in contact with a cutting edge and a second relief surface extending from the first relief surface and having a relief angle larger than a relief angle of the first relief surface. 
     
     
         9 . The insert of  claim 6 , wherein a central point angle between the central relief surfaces of the plurality of cutting parts is set to be 140° or less, and an outer circumferential point angle between the outer circumferential relief surfaces of the plurality of cutting parts is set to be 140° or more, wherein the outer circumferential point angle is defined by tangential lines of the outer circumferential relief surfaces meeting the outer circumferential surface. 
     
     
         10 . The insert of  claim 9 , wherein despite change in a size of an outer diameter of the drill, the outer circumferential point angle is set to be constant by changing at least one selected from a radius of the curved surface of each of the outer circumferential relief surfaces and a length of each of the central relief surfaces in a direction toward the outer circumferential surface.